Trench boxes providing barriers against cave-in are used extensively and, although constructed of heavy gauge material, are subject to failure and can rarely be used more than once. Moreover, because of the heavy gauge sheet material of which they are constructed, they are expensive and difficult to handle. It is the purpose of this invention to provide a trench box of relatively light gauge metal so reinforced as to efficiently resist failure due to lateral pressure. Further objects are to lower the initial cost of the structure, reduce its overall weight so as to enable easier handling and placement and to provide a structure which can be used repeatedly.